1. Field:
The subject matter disclosed herein relates to data transmission systems. In particular, the subject matter disclosed herein relates to the transmission of data frames in data links.
2. Information:
Local area networks (LANs) have enabled enterprises to operate data communication networks enabling devices such as personal computers, printers, data servers and the like to exchange data over a locally maintained transmission medium. Data links to couple these devices in a LAN typically transmit data between devices according any one of several Ethernet protocols provided in versions of IEEE Std. 802.3. Wide area networks (WAN) have enabled enterprises to couple LANs at different geographical sites to communicate by coupling the LANs by one or more high-speed data links. Such high-speed data links may be provided by a data communication service provider such as a telecommunication service provider. These high speed data links are typically part of a network backbone and formed according to the “Synchronous Optical NETwork” (SONET) protocol as indicated in a set of standards provided by the American National Standards Institute (ANSI T 1.105.xx) or “Synchronous Digital Hierarchy” (SDH) protocol as indicated in a set of recommendations provided by the International Telecommunications Union (e.g., ITU-T G.707, G. 708, G.709, G.783 and G.784).
In transmitting data between LANs, SONET links may encapsulate Ethernet frames in SONET for transmission between access ports on respective LANs. For example, an access port on a LAN may be adapted to transmit and receive data frames at a data rate of about 10 gigabits per second according to the 10 Gigabit Ethernet standard as provided in IEEE Std. 802.3ae-2002. The access port may then be coupled to a SONET link provisioned to provide data rate of about OC-192 capable of transmitting the encapsulated data frames at a data rate of about 9.5 gigabits per second.
FIG. 1 shows schematic diagram of a prior art access port 10 to initiate transmission of a pause request frames to a data source in response to the contents of a transmit buffer 12. On a LAN side, media access controllers 18 control the transmission of Ethernet frames to a WAN. Coupled to the WAN are a data transmitter 14 to transmit Ethernet frames encapsulated in SONET frames and a data receiver 16 to receive Ethernet frames capsulated in SONET frames. The data transmitter 14 and data receiver 16 each comprise an Ethernet MAC and a WAN interface sublayer (WIS) to encapsulate Ethernet frames in and de-encapsulate Ethernet frames from SONET frames as provided in IEEE Std. 802.3ae-2002, clause 50.
To prevent egress traffic from the LAN from overrunning the WAN's capacity to transmit data, a transmit buffer 12 may store Ethernet frames for transmission to the WAN. A flow control device 22 may also transmit a pause frame request to the LAN to request suspending the transmission of Ethernet frames for a predetermined period in response to the transmit buffer being full. Such a pause frame request may be provided as provided in IEEE Std. 802.3-2000, Clause 30.